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Old 03-24-2010, 11:11 AM
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ST-10 synchronizer options

Well, since I was a *bit* hard on my transmission last year, 3rd gear synchro is starting to show signs of giving up the ghost (it'll jump out of gear on deceleration - moreso when downshifting from 4th instead of upshifting from 1st or 2nd). So since I'll have to RnR the trans anyway, what are some options when it comes to blocker rings?

From what I've seen it looks like only brass is available, but don't know if there is something I haven't found or if it's even something that I need to worry about. The car in question is a 1978 Trans Am that is mainly a street car with some occasional track time (it's still the original ST-10 that I had rebuilt 8 or 9 years ago).

Thanks,
Mike

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Old 03-26-2010, 12:47 PM
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Hmmm, I'm gonna guess that the sound of crickets means that nobody knows, or that brass is more'n enough for my needs . . .

OK.
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Old 03-26-2010, 07:15 PM
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I haven't looked in a while but I don't think there is anything other than brass offered unless you send it out for a Pro-shift conversion to dog type syncro's.

Nothing wrong at all with new brass, it is usually the other parts of the syncro assembly like the slider or the engagement teeth on the gear that are the problem you are describing. Just a rebuild with new brass blocker rings may not fix your problem. The jumping back out of gear is a misadjusted stop on the shifter or the engagement teeth on the gear or slider are worn too much. The engagement teeth on the slider are tapered back cut to prevent this jumping out, but if worn too much it will happen. It will also happen if the shifter doesn't push the slider far enough together to catch this back cut portion.

All you can do is take it out and disassemble it to look over all the engagement areas for wear.

If the trans isn't grinding on an upshift or down shift it is not likely to be a blocker ring problem. Look at the shifter adjustment first, Hurst Comp Plus shifter body's have adjustable stops and yours may be out of adjustment, or the shifter arms and rods may just need new bushings.
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Old 04-05-2010, 07:26 PM
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Yea, I'm not interested in dog'ing the synchros on a mainly street-driven vehicle. I did find a rollerized mainshaft when looking at rebuilt kits years ago, but didn't pony up the bucks for it.

I can tell you the exact time and cause of the 3rd gear issues I'm having - it was when I had a mild brain-fart and got my clutch-shift-clutch process out of whack when shifting from 2nd to 4th - with the very ugly and very loud result of grinding 4th gear. Right after this happened, 3rd gear wouldn't engage *at all*, no-way, no-how unless you really kept pressure on the shifter. My initial thought was that the . . . mis-step . . . in 4th knocked one of the 3-4 clutch keys out of alignment and was preventing 3rd gear from engaging. I parked it after that for the winter with thoughts of tearing into it to find the real cause, but never did look into it. Course now 3rd is working as mentioned before, so don't know why it partially fixed some issues over winter itself.

When I first bought the car, it was having 2nd gear synchro issues thanks to the previous owner. I had rebuilt it back then and fixed the 2nd gear issue with a rebuild kit and new brass rings (my first transmission rebuild ever). Course, whoever had it before me didn't know how to handle the non-synchro'd reverse so the teeth on the reverse gears were more than 1/2-ground away, with the result of much metallic particulates in the trans case (yep, reverse was replaced with new). Guess I should be glad that this is the only real issue I've had with the trans. Oh yea, new shifter bushings had been installed back in the spring (Hurst Pit Pack), but the shifter is still a bit sloppy - directly linked to the wear on the shift forks and sliders, I'll bet.

Guess it's time for new sliders and forks, at a minimum (I have no idea how many miles are actually on the drivetrain, but I'm pretty sure the engine still has it's stock internals).
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Old 04-05-2010, 07:43 PM
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Sounds like it could also be that the main body of the Hurst shifter needs to be rebuilt or replaced, they do wear out and get sloppy. Hurst used to have a pretty inexpensive rebuild service for the shifter body, made them good as new, but last time I looked the price on this service had more than tripled, to the point it wasn't a whole lot more to just get a whole new Comp Plus shifter.
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